I've seen assignments that were clearly graded by ChatGPT. The signs are obvious: suggestions that are unrelated to the topic or corrections for points the student actually included. But of course, you can't 100% prove it. It's creating a strange feedback loop: students use an LLM to write the essay, and teachers use an LLM to grade it. It ends up being just one LLM talking to another, with no human intelligence in the middle.
However, we can't just blame the teachers. This requires a systemic rethink, not just personal responsibility. Evaluating students based on this new technology requires time, probably much more time than teachers currently have. If we want teachers to move away from shortcuts and adapt to a new paradigm of grading, that effort needs to be compensated. Otherwise, teachers will inevitably use the same tools as the students to cope with the workload.
Education seemed slow to adapt to the internet and mobile phones, usually treating them as threats rather than tools. Given the current incentive structure and the lack of understanding of how LLMs work, I'm not optimistic this will be solved anytime soon.
I guess the advantage will be for those that know how to use LLMs to learn on their own instead of just as a shortcut. And teachers who can deliver real value beyond what an LLM can provide will (or should) be highly valued.